1. Field of the Invention
The present invention relates to network technology and more particularly, to a network signal coupling circuit, which uses coupling modules to enhance the signal coupling performance subject to the characteristic of capacitors that the strength increases when the frequency rises.
2. Description of the Related Art
Following fast development of computer technology, desk computers and notebook computers are well developed and widely used in different fields for different applications. It is the market trend to provide computers having high operating speed and small size. Further, network communication technology brings people closer, helping people to gather information about living, learning, working and recreational activities. By means of network communication, people can communicate with one another to send real time information, advertising propaganda or e-mail. Further, through the Internet, people can search information, send instant messages, or play on-line video games. The development of computer technology makes the relationship between people and network unshakable and inseparable.
Connecting a computer or electronic apparatus to a network for data transmission can be done by a cable connection technique or a wireless transmission protocol. A cable connection technique needs the installation of a network connector. A conventional network connector has built therein transformer modules and common-mode suppression modules. As shown in FIG. 5, a conventional network connector comprises a circuit board A, and multiple transformer coils B and filter coils C installed in the circuit board A. Each of the transformer coils B and filter coils C comprises a wire core D, and a lead wire D1 wound round the wire core D with the ends thereof bonded to respective contacts at the circuit board A. Because the winding of the transformer coils B and the filter coils C cannot be achieved by an automatic machine and must be done by labor, the fabrication efficiency of this kind of network connector is low. Further, the lead wire may be broken easily during winding, thereby increasing the cost. Further, fabrication by labor cannot accurately control the coil winding tightness and number of turns, affecting product quality stability.
Further, following the development of network application technology, network data transmission capacity has been greatly increased. To satisfy the demand for high data transmission capacity, network transmission speed has been greatly improved from the early 10 Mbps to 100 Mbps or 1 Gbps. Nowadays, fiber-optic network transmission speed can be as high as 10 Gbps and up. A transformer coil B is an inductor, the impedance (Z) of an inductor is an inductive reactance, and its unit is ohm (a). The inductive reactance is calculated subject to the equation of Z=2π*f*L), in which: f=frequency and its unit is hertz (Hz); L=inductance of inductor and its unit is Henry (H). The aforesaid network connector utilizes the characteristic of the inductance of the transformer coils B to isolate electricity and to couple signals. In order to transmit signals from the primary side to the secondary side, each transformer coil B must have a predetermined inductance. From the above equation, it is known that inductive reactance is directly proportional to the working frequency and the inductance of the inductor. When increasing the signal frequency, the inductance reactance will be relatively increased (see the comparative curve of frequency and capacitive reactance based on a 350 μH capacitor shown in FIG. 6). However, increased inductive reactance causes increased signal attenuation, leading to network disconnection or dramatic slowdown in network transmission speed. As shown in FIG. 7, when the insertion loss of the transformer reaches −3 db, the response frequency becomes 0.45 MHz˜240 MHz. When over this range, the insertion loss will increase rapidly. Therefore, the working frequency must be controlled within a relatively narrower bandwidth. Further, subject to the characteristic curve of the transformer coils B of low frequency with low strength, middle frequency with high strength and high frequency with low strength, when the network transmission speed reaches 1 Gbps, the signal strength of the transformer coils B will be lowered, unable to meet the product requirements.
Therefore, there is a strong demand for a network signal coupling circuit, which eliminates the drawbacks of instable quality, high cost, automated production incapability and low signal strength under a high network transmission speed of the prior art network connector design.